IRIS is NASA's Interface Region Imaging Spectrograph and was built by Lockheed Martin Solar and Astrophysics Laboratory (LMSAL) in CA, USA. It was launched on June 27, 2013 into a Sun-synchronous orbit and contains a 19 cm UV telescope along with a slit based dual-bandpass imaging spectrograph and described in [1]}.
IRIS observes the interface region between the relatively cool (6,000 K; photosphere) solar surface and the hot (\(\approx \)  millions of degrees; corona) outer atmosphere. It takes images in four different wavelengths in the ultraviolet range. These passbands are each sensitive to plasmas of different temperatures: Mg II wing (2830 Å, 6,000 K), Mg II k (2796 Å, 10,000 K), C II (1330 Å, 25,000 K), Si IV (1400 Å, 80,000 K). The IRIS mission includes a detail analysis of this highly structured and complex interface region with strong radiative-MHD codes. The importance of this interface region relies on the fact that the mechanical energy, which is a driver of solar activity and solar atmospheric heating, is converted into radiation and heat in this region. A small amount of energy leaks from this region through the coronal heating and accelerating solar wind. The transition between low to high plasma \(\beta \)  occurs in between of the photosphere and corona. Therefore in the interface region, there is always a competition between the plasma and the magnetic field for dominance. This race between plasma and magnetic field yields various impacts e.g. wave generation, mode coupling, reflection, and refraction. The evidence for the supersonic and super Alfvénic motions is provided by the plasma flow from partially ionized chromosphere to fully ionized corona. Non local thermodynamic equilibrium (non-LTE) effects dominate the radiative transfer in the partial opaque chromosphere. In this way to explain the radiation process and to determine the energy balance state needs advanced computer modelling. Hence the high cadence observational data is required.
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